The present invention relates to compressed video processing, and more particularly to a method of rate and delivery time multiplexing for bandwidth optimization.
In the transmission of video signals over physical transmission links, or pipes, the desire is to transmit as many of such video signals as possible through the pipes. To accomplish this objective video compression techniques, such as JPEG or MPEG, are used. These compression techniques are lossy in that some degradation of the video signal occurs between the encoding and decoding of the video signals. Thus the amount of compression a video signal is subjected to is a tradeoff between bandwidth and picture degradation, or what an end user or subscriber will tolerate. If the picture is compressed too much, the subscriber will object to the picture degradation. If the picture is not compressed enough, then the number of video signals that may be transmitted over the pipe is not optimized. The more complex the picture, the more bandwidth is required to avoid undesirable amounts of picture degradation.
For transmission networks optical fiber pipes provide wide bandwidth so that many video signals may be transmitted over great distances simultaneously. This optical physical medium generally is used for the backbone of the transmission network, but does not cover the “last mile” to the subscriber's location. This last mile is generally completed using a copper connection, such as twisted pair telephone cables. The bandwidth of the copper connection, or pipe, is much less than that of the optical pipe, and any signals in the copper pipe attenuate rapidly with distance. For example, very high bit rate digital subscriber line (VDSL) technology supports very high bit rates, up to 55 Mbps downstream from a head end to a subscriber and 19 Mbps upstream from the subscriber to the head end, and is intended for deployment over relatively short copper loops of 1000 to 4000 feet. On the other hand asymmetric digital subscriber line (ADSL) technology allows the use of one existing twisted pair local loop to provide high bandwidth data and/or video services. ADSL supports two-way transmission of analog voice (plain old telephony service —POTS), a downstream-only digital broadband channel of up to 9 Mbps for data or video distribution, and an upstream-only digital channel of up to 640 Kbps. ADSL deployment may be used over a range up to 12,000 feet, but is typically used for data only or only one video signal.
With VDSL technology current service providers are able to transmit to a single subscriber up to three video signals simultaneously. However only those subscribers close to the head end or a remote terminal may benefit from this technology. What is desired is to be able to provide the same ability of transmitting up to three video signals per subscriber on a physical transmission medium having less bandwidth so as to cover more subscribers over a greater area.
In the MPEG compression scheme every outgoing byte of data belongs to a transport stream packet, and for every program in the transport stream every outgoing byte has a time associated with that transport stream's clock. Thus if there are ten programs, every byte has one of ten different times, each one associated with a different program clock. (See Section 2.4.2.2 of ISO 13818-1 for details). In addition every byte has a time associated with its output clock. GOP refers not only to a group of pictures, but also to a complete sequence when there is no group of pictures—such is the case with video from some content services, such as HITS, where each new sequence is 15 pictures in length and has no I frames, only P and B frames with intra-coded slices ordered as PBBPBBPBB . . .
There is a fixed bandwidth pipe which supports a constant number of MPEG Transport Stream (MTS) packets per second. There are N single program transport streams as input, either variable bit rate (VBR) or constant bit rate (CBR), which are required to be multiplexed into the CBR outgoing MTS. N is not necessarily a constant. The desire is to optimize N for the given MTS.